Use of short-loop electrical measurements for yield improvement

Modern submicron processes are more sensitive to both random and systematic wafer-level process variation than ever before. Given the dimensional control limitations of new technologies, the amount of wafer-to-wafer and within wafer nonuniformity of many steps is becoming a significant fraction of the total error budget, which already includes the usual step-to-step allocations. However, a significant portion of the total observed variability is systematic in nature. Accordingly, particle defects may not continue to dominate parametric yield loss without improved understanding of parametric variations. In this paper, we demonstrate the use of short-loop electrical metrology to carefully characterize and decouple wafer-level variability of several critical processing steps. More specifically, we present our method and give results obtained from variability analyses for lithography critical dimension (CD) and inter-level dielectric (ILD) thickness control. Using statistically designed experiments and dedicated test structures, the main factors affecting dielectric thickness variability has been identified. The systematic variability from a wafer stepper has been extracted using a physically based statistical data filter. Once isolated, the deterministic variability can be modeled and controlled to enhance process and circuit design for manufacturability (DFM). We hope that in the future this work will be coupled with novel DFM-oriented CAD tools that encapsulate this information in a fashion that makes it useful to process and circuit designers.<
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